I’ll have our Michael Cassio on the hip,
Abuse him to the Moor in the rank garb –
For I fear Cassio with my night-cap too.
– William Shakespeare
Othello, Act 2, Scene 1. As he plots revenge, Iago suspects that Cassio has slept with his wife Emilia. Just as he thinks Othello has done the same, without having any proof. This suggest insecurity and paranoia on the part of Iago. "With my night-cap" is a metaphor for sleeping with someone. Iago’s jealousy of and hatred for Cassio are evident here.